Untersuchungen über die Flimmerschwelle des isolierten Meerschweinchen-Herzens für Gleichstrom und sinusförmigen Wechselstrom

Abstract

In isolated perfused guinea-pig hearts the threshold for ventricular fibrillation was determined applying DC or sinusoidal 50-cycle AC pulses during the vulnerable period. The results were compared with the threshold for single responses during diastole.Using rectangular pulses from 0.5 to 40 msec the threshold for fibrillation as well as for single responses exhibited a nearly linear relationship between strength and duration of impulses when plotted in a log-log-scale. As compared with the threshold for single responses the fibrillation threshold was shifted in parallel to a higher intensity level.Vulnerability of the ventricles was independent on stimulus duration. When the hearts were beating in AV-rhythm maximal vulnerability appeared about 150 msec after the beginning of ventricular excitation.Alteration of the physical conditions by increasing the magnitude ~f the electrodes and changing their position resulted in an increase of the threshold for single diastolic responses accompanied by a decrease of the fibrillation threshold, both curves being shifted in parallel retainig their slope. Using the same electrode arrangement, the threshold for electrical defibrillation exhibited a similar characteristic as the fibrillation threshold, however on a higher intensity level.With sinusoidal 50-cycle AC pulses an increase of stimulus duration beyond 1 period caused no further change to the threshold for single responses, whereas the threshold for fibrillation declined continously until a total duration of about 6 periods was attained.The results are interpreted in terms of the re-entry mechanism of fibrillation.Die Wirksamkeit des elektrischen Stroms f(ir die Ausl6sung yon Vorhofbzw. Kammerflimmern des Herzens ist von zahlreichen physikalischen und biologischen Gegebenheiten abh~ingig (14, 24, 26, 29, 36, 41, 42). Als physikalische Bedingungen kommen haupts~ichlich in Betracht:1. die Stromdichte im Herzen: Sie ist abh/ingig yon der angelegten Spannung, der Gr61~e und Position der Elektroden und den Widerstands-verhMtnissen

Factors determining the susceptibility of the isolated guinea pig heart to ventricular fibrillation induced by sinusoidal alternating current at frequencies from 1 to 1000 Hz

“…Moreover, in the isolated heart perfusion continues during fibrillation, whereas in the intact animal the coronary circulation is strongly reduced by the arrhythmias, rendering frequent measurements of the fibrillation threshold impossible. Although in the guinea pig heart fibrillation is usually transient, the basic mechanism of its induction and development is not different from that found for the hearts of larger animals (2,11,16,25).…”

“…As compared with the hearts of larger animals (sheep, dogs and pigs), the guinea pig heart tends to defibrillate spontaneously (16,25). Hence possible injury of the preparation due to electrical defibrillation is avoided.…”

Influence of direct current on the electrical activity of the heart and on its susceptibility to ventricular fibrillation

“…I n p r e c e d i n g s t u d i e s a c o n t i n u o u s d e c l i n e of t h e t h r e s h o l d for fibrillat i o n w a s f o u n d w i t h i m p u l s e d u r a t i o n s of u p to 40 m s (17). T h i s l e d us to e x a m i n e w h e t h e r t h e f i b r i l l a t o r y e f f i c a c y of t h e D C is f u r t h e r i n c r e a s e d if t h e r a n g e of i m p u l s e d u r a t i o n s is e x t e n d e d u p to a b o u t 100 ms,…”

“…The threshold for fibrillation was determined by Younossi et al (17) in isolated guinea pig hearts using DC pulses between 0.5 and 40 ms. These studies revealed a nearly hyperbolic function comprising the range of impulse strengths between about 15 and i00 mA.…”

Mikrocomputer-gesteuerte 3-Kanal-Stimulationseinrichtung zur Analyse der atrialen und ventrikulären Vulnerabilität des Herzens - A Microcomputer-Controlled 3-Channel Stimulator for Investigating Atrial and Ventricular Vulnerability of the Heart

“…von *) Deutsche Forschungsgemeinschaf t Gu 173/2 -1979. Stromimpulsserien) [2,3, 5,6,7,9,10,11,12,13,14,16,17,18]. Die biologische Bedeutung der angegebenen Stimulationsmethoden und die Übertragbarkeit der hiermit erhaltenen Ergebnisse auf Pathogenese und Therapie spontaner Arrhythmien sind zur Zeit Gegenstand klinischer und experimenteller Forschung.…”